1. Field of the Invention
The present invention relates generally to balloon angioplasty for dilating obstructed blood vessels, and more particularly to an improved balloon-tipped catheter which provides for convectively heating a gas volume within the balloon to promote healing and sealing of damage which may occur to the interior wall of the vessel.
Balloon angioplasty was first described by Andreas Gruntzig in 1977. Dr. Gruntzig employed a balloon-tipped flexible catheter to percutaneously dilate a region of stenosis within the coronary artery of a patient with atherosclerotic coronary artery disease. Since the original work, the use of percutaneous balloon angioplasty has become widespread, with treatment of occluded peripheral blood vessels as well as coronary arteries.
Conventional balloon angioplasty compresses the plaque outwardly into the vessel wall. Such outward compression results in stress on the vessel wall, often causing cracking, tearing and stretching of the wall. In some cases, after the balloon catheter is removed, torn plaque and tissue become dislodged from the vessel wall resulting in abrupt reclosure of the vessel. Even when such abrupt reclosure does not occur, it is thought that the irregular inner surface of the vessel wall (which results from the cracking and tearing) may contribute to restenosis at the same location within the vessel. For these reasons, it would be desirable to provide a method for sealing the torn tissue and plaque to the vessel wall to provide a smooth interior surface which will not be subject to reclosure or restenosis.
One approach for promoting the healing of blood vessels damaged by balloon angioplasty has been proposed by Dr. Richard Spears and his colleagues at the Beth Israel Hospital, Harvard Medical School, Boston, Massachusetts. They proposed the use of dispersed laser radiation to promote healing and sealing of the injured vessel wall. Specifically, their technique requires that a dispersion lens be placed inside the dilation balloon, and that a Nd-YAG laser be connected to the lens by a fiber optic waveguide extending the length of the catheter. While the balloon is dilated, the laser source is activated, resulting in direct irradiation of the interior wall of the blood vessel through the balloon wall.
While Dr. Spears' technique offers many advantages, it also suffers from certain drawbacks. First, the optics required to disperse the laser radiation are only effective over relatively short distances on the order of about 10 mm. Since the length of the angioplasty balloon can be as much as 10 cm (in the case of some peripheral vessels), it becomes impractical to treat the entire length of a damaged vessel wall in a single step. Second, the outer surface of the dilation balloon is covered with blood and often becomes clouded and opaque as the balloon is inserted in the vessel and dilated to expand the stenosed region. Such obscuring of the surface can limit the transmission of the laser radiation through the balloon wall, reducing or preventing healing of the vessel wall. Third, it appears that the laser radiation, which is of a relatively high energy, has an effect on the nature of the interior of the vessel wall. The long term significance of such effects are not yet known.
For the above reasons, it would be desirable to provide methods and apparatus for promoting the healing and restoration of the interior wall of blood vessels damaged by balloon angioplasty. In particular, it would be desirable to provide such methods where the entire length of the vessel contacted by the balloon can be treated in a single step, where the treatment is unaffected by occlusion and obscuring of the outer surface of the angioplasty balloon, and where treatment does not degrade or otherwise affect the nature of the tissue on the interior of the vessel wall.
2. Description of the Prior Art
The basic technique of balloon angioplasty is taught in U.S. Pat. No. 4,195,637 to Gruntzig et al. Certain aspects of the use of Nd-YAG laser radiation to promote healing and sealing of injured blood vessel walls, as described hereinabove, are set forth in Hiehle, Jr., et al. (1985) Am. J. Cardiol. 15:953-957. U.S. Pat. No. 4,470,407 to Hussein discloses an endoscopic device having a laser beam terminating inside a balloon. The laser beam, which is directed through the wall of the balloon, is intended to illuminate and treat the interior of the wall of the vessel. The exact nature of the treatment is not made clear. Sanborn et al. (1985) J. Am. Coll. Cardiol. 5:934-938 discloses the use of a laser-heated metallic cap on a fiber optic tube, where the heated cap is used to destroy stenotic obstructions in blood vessels.